Sarunas designed this RC receiver replacement which uses a smart phone as remote controller via WiFi or Bluetooth:

Smart Racer

Why not control your RC car with smart phone?

Features include:

• Control RC car from Android phone or iPhone
• Control RC servo and ESC
• Control 5 Leds
• Drive RC car up to 70m away
• Drives Brushed and Brushless motors
• Works with 1:10 and 1:18 models
• Powered directly from ESC power
• Control using REST API
• Connection lost cut off

The design files and source code are available on GitHub:

Here’s the Smart Racer in action: